Heat sink



FIG. 1 is a front side elevation view thereof;

FIG. 2 is a rear side elevation view thereof;

FIG. 3 is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a top plan view thereof; and

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view of a heat sink showing my new design. 

The ornamental design for a heat sink, as shown and described. 